Imaging lens

ABSTRACT

An imaging lens includes a first lens having negative refractive power; a second lens having negative refractive power; a third lens having positive refractive power; a fourth lens having positive refractive power; and a fifth lens having negative refractive power. The first lens has object-side and image plane-side surfaces with positive curvature radii. The second lens has object-side and image plane-side surfaces with positive curvature radii. The third lens has an object-side surface with a positive curvature radius and an image plane-side surface with a negative curvature radius. The fourth lens has an object-side surface with a positive curvature radius and an image plane-side surface with a negative curvature radius. The fifth lens has object-side and image plane-side surfaces with negative curvature radii. The first to fifth lenses have specific Abbe&#39;s numbers to satisfy specific conditions. The fifth lens has a specific focal length to satisfy specific conditions.

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT

The present invention relates to an imaging lens for forming an image ofan object on an imaging element such as a CCD sensor and a CMOS sensor,and particularly, it relates to an imaging lens suitable for mounting ina relatively small camera such as a cellular phone, a digital stillcamera, a portable information terminal, a security camera, a vehicleonboard camera, and a network camera.

In these years, in order to enhance convenience and improve security, aplurality of cameras is mounted on a vehicle. For example, in case of avehicle equipped with a rear-view camera to take an image behind thevehicle, the view behind the vehicle is shown on a monitor when a driverdrives the vehicle backward. Accordingly, the driver can safely drivethe vehicle backward without contacting obstacles that cannot bedirectly seen by the driver. Such cameras for mounting on vehicles,i.e., so-called onboard cameras, are expected to increase in popularity.

Generally speaking, an onboard camera is often accommodated in arelatively small space such as in a back door, a front grille, a sidemirror, and inside of the vehicle. For this reason, in addition to asmall size, an imaging lens for mounting on the onboard camera isrequired to be suitable for a high resolution accompanied by anincreased number of pixels of an imaging element and a wider angle totake in a broad range. However, it is difficult to achieve a small sizeand a high resolution as well as a wide imaging angle, while properlycorrecting aberrations. For example, when a size of an imaging lens isreduced, refractive power of individual lens tends to become stronger.Accordingly, it is difficult to satisfactorily correct aberrations.Therefore, upon actually designing an imaging lens, it is important tomeet those requirements in a well-balanced manner.

As an imaging lens with a wide imaging angle, for example, PatentReference has disclosed a conventional imaging lens. The conventionalimaging lens includes a negative first lens that has a shape of ameniscus lens directing a convex surface thereof to the object side, asecond lens having a biconcave shape, a third lens having a biconvexshape, an aperture stop, a fourth lens having a biconvex shape, and anegative fifth lens that has a shape of a meniscus lens directing aconcave surface thereof to the object side, arranged in this order froman object side.

According to the conventional imaging lens disclosed in PatentReference, the third lens and the fifth lens in the configuration areformed of a high-dispersion material. Accordingly, it is possible tocorrect a field curvature and a chromatic aberration of magnification.Further, the second lens is formed in a shape of a biconcave lens nearan optical axis thereof to achieve a wide angle, thereby increasingnegative refractive power.

Patent Reference: Japanese Patent Application Publication No.2011-107593

According to the conventional imaging lens described in PatentReference, although the number of lenses that compose the imaging lensis as few as five, an imaging angle of view is wide and it is possibleto relatively satisfactorily correct aberrations. In the conventionalimaging lens, however, a total length of the whole lens system tends tobecome long relative to a focal length. Accordingly, it is difficult toachieve a small size. In these days, there remain issues to achieve bothdownsizing of the imaging lens and satisfactory correcting aberration.Here, such an issue is not a problem specific to the imaging lens formounting on onboard cameras. Rather, it is a common problem for animaging lens to accommodate in a relatively small camera such ascellular phones, digital still cameras, portable information terminals,security cameras, and network cameras.

In view of the above-described problems in conventional techniques, anobject of the present invention is to provide an imaging lens that haswide imaging angle of view and can satisfactorily correct aberrations inspite of a small size thereof.

Further objects and advantages of the present invention will be apparentfrom the following description of the present invention.

SUMMARY OF THE INVENTION

In order to attain the objects described above, according to a firstaspect of the invention, an imaging lens includes a first lens havingnegative refractive power; a second lens having negative refractivepower; a third lens having positive refractive power; a fourth lenshaving positive refractive power; and a fifth lens having negativerefractive power, arranged in this order from an object side to an imageplane side.

According to the first aspect of the present invention, the first lenshas an object-side surface and an image plane-side surface, curvatureradii of which are both positive. The second lens has an objectside-surface and an image plane-side surface, curvature radii of whichare both positive. The third lens has an object-side surface, acurvature radius of which is positive, and an image plane-side surface,a curvature radius of which is negative. The fourth lens has anobject-side surface, a curvature radius of which is positive, and animage plane-side surface, a curvature radius of which is negative. Thefifth lens has an object-side surface and an image plane-side surface,curvature radii of which are both negative. Each of the first throughthe fourth lenses is made of a material having Abbe's number of between45 and 75. The fifth lens is made of a material having Abbe's number of20 to 40.

According to the first aspect of the present invention, when the wholelens system has a focal length f and the fifth lens has a focal lengthf5, the imaging lens satisfies the following conditional expression (1):

−1.5<f5/f<−0.5  (1)

According to the first aspect of the present invention, in the imaginglens, each of the first through the fourth lenses is made of a materialhaving Abbe's number of between 45 and 75 and the fifth lens is made ofa material having Abbe's number of 20 to 40. Therefore, since Abbe'snumbers of those four of the five lenses are larger than the lower limitof “45”, it is possible to effectively restrain chromatic aberrationsgenerated in those four lenses and suitably restrain a chromaticaberration of the whole lens system within suitable range. In addition,having the upper limit of the Abbe's number of each lens smaller than“75”, it is possible to restrain cost of the lens materials.

In order to achieve a wide angle, according to the first aspect of thepresent invention, the imaging lens is provided with two lenses havingnegative refractive powers on the object side. With this configuration,it is possible to achieve a wide angle while keeping refractive powersof the two lenses having negative refractive powers, i.e., the firstlens and the second lens. This is effective even in view of reducingproduction error sensitivity of the imaging lens. As the angle becomeswide, however, it matters how to correct a distortion and a fieldcurvature. According to the first aspect of the present invention, inthe imaging lens, only one lens is made of a high-dispersion materialamong the five lenses. Accordingly, the role of the fifth lens is moresignificant than that in a conventional imaging lens. The fifth lens isa lens provided most closely to the image plane in the imaging lens.

When the imaging lens satisfies the conditional expression (1), it ispossible to restrain the field curvature within satisfactory range,while correcting a distortion and a chromatic aberration. When the valueexceeds the upper limit of “−0.5”, since the fifth lens has relativelystrong refractive power relative to that of the whole lens system, it iseasy to correct negative distortion, which is easily generated as theangle of view is widen, and it is easy to restrain insufficientcorrection of an axial chromatic aberration (a focal point at a shortwavelength moves towards the object side relative to a focal position ata reference wavelength). However, a periphery of the image-formingsurface curves to the image plane side. Accordingly, it is difficult torestrain the field curvature within satisfactory range. For this reason,it is difficult to obtain satisfactory image-forming performance.

On the other hand, when the value is below the lower limit of “−1.5”,the axial chromatic aberration is insufficiently corrected and achromatic aberration of magnification is also insufficiently corrected(an image-forming point at a short wavelength moves in a direction to beclose to the optical axis relative to an image-forming point at areference wavelength). In addition, since negative distortion alsoincreases, it is difficult to obtain satisfactory image-formingperformance.

According to a second aspect of the present invention, in the imaginglens in the first aspect, when the first lens has a focal length f1 andthe second lens has a focal length f2, the imaging lens preferablysatisfies the following conditional expressions (2) and (3):

−3.5<f1/f<−1.5  (2)

1.0<f1/f2<1.5  (3)

When the imaging lens satisfies the conditional expression (2), it ispossible to reduce the size of the imaging lens, while restraining anincident angle of a light beam emitted from the imaging lens to animaging element. As well known, an imaging element such as a CCD sensoror CMOS sensor has a so-called chief ray angle (CRA) set in advance,i.e. range of an incident angle of a light beam that can be taken in thesensor. By restraining an incident angle of a light beam emitted fromthe imaging lens to an image plane within the CRA range, it is possibleto suitably restrain generation of shading, a phenomenon of dark imageperiphery.

When the value exceeds the upper limit of “−1.5” in the conditionalexpression (2), since the imaging lens has a long back focal length,while it is easier to restrain an incident angle of a light beam emittedfrom the imaging lens to an imaging element, it is difficult to achievedownsizing of the imaging lens. In addition, since the imaging-formingsurface curves to the object side, it is difficult to obtainsatisfactory image-forming performance. On the other hand, when thevalue is below the lower limit of “−3.5”, since the back focal length isshort, although it is advantageous for downsizing of the imaging lens,it is difficult to secure space to place an insert such as an infraredcutoff filter. Furthermore, an incident angle of a light beam emittedfrom the imaging lens to the imaging element is large, so that it isdifficult to restrain generation of shading.

When the imaging lens satisfies the conditional expression (3), it ispossible to satisfactorily correct a distortion and an astigmatism,while achieving downsizing of the imaging lens. When the value exceedsthe upper limit of “1.5”, a position of an incident pupil moves to theobject side and the back focal length becomes long, and it is difficultto achieve downsizing of the imaging lens. Moreover, since the sagittalimage surface in the astigmatism curves to the image plane side and theastigmatic difference increases, and negative distortion also increases,it is difficult to obtain satisfactory image-forming performance.

On the other hand, when the value is below the lower limit of “1.0”, theincident pupil moves to the image plane side and the back focal lengthbecomes short, so that, although it is advantageous for downsizing ofthe imaging lens, the sagittal image surface in the astigmatism curvesto the object side and the astigmatic difference increases. Therefore,also in this case, it is difficult to obtain satisfactory image-formingperformance.

The conditional expressions (2) and (3) set the distribution ofrefractive powers of the first lens and the second lens in the imaginglens. When the imaging lens satisfies the conditional expressions (2)and (3), it is easier to correct aberrations generated in the third lensand thereafter, while achieving widening of an angle of view of theimaging lens. Moreover, when widening of an angle of view is made byincreasing refractive power of the first lens as in a typicalconventional imaging lens, the shape of a concave surface of the firstlens on an image plane side thereof becomes close to a semisphericalshape. However, by satisfying the conditional expressions (2) and (3)while widening an angle of view with the two negative lenses, i.e. thefirst and the second lenses, it is possible to suitably restrain thatthe concave surface of first lens on the image plane side thereofbecomes like a semispherical shape. Therefore, according to the secondaspect of the present invention, the imaging lens is easy to evenlyapply anti-reflection coating, etc., and it is possible to improve yieldupon production of the imaging lens.

According to the imaging lens having the above-described configuration,the first lens and the second lens preferably have weaker refractivepowers than each lens of the third lens to the fifth lens. When thefirst lens and the second lens have strong refractive powers, althoughit is easy to widen an angle, it is difficult to satisfactorily correctaberrations. In addition, the third lens preferably has weakerrefractive power than any of the fourth lens to the fifth lens. Asdescribed above, since the lens made of high-dispersion material is onlyone, i.e. the fifth lens, in the imaging lens of the present invention,it is preferred that the fourth lens and the fifth lens have strongrefractive powers also in view of correction of a chromatic aberration.

According to a third aspect of the present invention, in the imaginglens in the first aspect, an object-side surface of the second lens ispreferably formed in an aspheric shape so as to direct a convex surfacethereof to the object side near an optical axis and direct a concavesurface thereof to the object side at periphery of the lens. With such ashape of the object-side surface of the second lens, it is possible tomore satisfactorily correct a field curvature.

According to a fourth aspect of the present invention, in the imaginglens in the first aspect, when the third lens has a focal length f3 andthe distance along an optical axis between the second lens and the thirdlens is dA, the imaging lens having the above-described configurationpreferably satisfies the following conditional expressions (4) and (5):

0.5<f3/f<2.5  (4)

0.5<dA/f<1.0  (5)

When the imaging lens satisfies the conditional expression (4), it ispossible to satisfactorily correct the astigmatism and a chromaticaberration, while downsizing the imaging lens. When the value exceedsthe upper limit of “2.5”, the back focal length of the imaging lens islong and it is difficult to attain downsizing of the imaging lens. Inaddition, the axial chromatic aberration is excessively corrected (afocal position at short wavelength moves to the image plane siderelative to a focal position at a reference wavelength), and a chromaticaberration of magnification is insufficiently corrected. In this case,negative distortion also increases and it is difficult to obtainsatisfactory image-forming performance. On the other hand, when thevalue is below the lower limit of “0.5”, since the back focal length isshort, although it is advantageous for downsizing of the imaging lens,an axial chromatic aberration is insufficiently corrected.

In addition, in case of an off-axis light beam entering in periphery ofthe image plane, since an image-forming surface at a short wavelengthmoves to the object side, flare is generated by so-called image surfacedisplacement, and it is difficult to obtain satisfactory image-formingperformance.

When the imaging lens satisfies the conditional expression (5), it ispossible to satisfactorily a correct distortion, an astigmatism, and achromatic aberration, while downsizing the imaging lens. When the valueexceeds the upper limit of “1.0”, although it is advantageous forcorrection of an axial chromatic aberration, the total length of thewhole lens system and the back focal length become long, and it isdifficult to reduce a size of the imaging lens. Moreover, since negativedistortion increases and inward coma aberration is generated in off-axislight beam entering periphery of the image plane, it is difficult toobtain satisfactory image-forming performance.

On the other hand, when the value is below the lower limit of “0.5”,since the axial chromatic aberration is insufficiently corrected and thesagittal image surface in the astigmatism and an image-forming surfaceat a short wavelength curve to the object side, it is difficult toobtain satisfactory image-forming performance.

The third lens is a lens disposed most closely to the object side amongthe lenses having positive refractive powers, and is disposed behind thetwo negative lenses (on the image plane side), the first lens and thesecond lens. The position and the refractive power of the third lens inthe imaging lens are important also for satisfactory correction ofaberrations. When the imaging lens satisfies the conditional expressions(4) and (5), it is possible to satisfactorily correct aberrations whileattaining downsizing of the imaging lens.

According to the present invention, the imaging lens is especiallyeffective for an imaging lens that is required to have an angle of viewof at least 120° (120°≦2ω).

According to the present invention, it is possible to attain both a wideangle of view and the satisfactory aberration correction of the imaginglens, and it is possible to provide the small-sized imaging lens withsatisfactorily corrected aberrations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a sectional view of a schematic configuration of an imaginglens in Numerical Data Example 1 according to an embodiment of thepresent invention;

FIG. 2 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 1;

FIG. 3 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 1;

FIG. 4 shows a sectional view of a schematic configuration of an imaginglens in Numerical Data Example 2;

FIG. 5 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 4;

FIG. 6 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 4;

FIG. 7 shows a sectional view of a schematic configuration of an imaginglens in Numerical Data Example 3;

FIG. 8 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 7;

FIG. 9 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 7;

FIG. 10 shows a sectional view of a schematic configuration of animaging lens in Numerical Data Example 4;

FIG. 11 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 10;

FIG. 12 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 10;

FIG. 13 shows a sectional view of a schematic configuration of animaging lens in Numerical Data Example 5;

FIG. 14 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 13; and

FIG. 15 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 13.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereunder, referring to the accompanying drawings, an embodiment of thepresent invention will be fully described.

FIGS. 1, 4, 7, 10, and 13 are schematic sectional views of imaginglenses in Numerical Data Examples 1 to 5 according to the embodiment,respectively. Since a basic lens configuration is the same among thoseNumerical Data Examples, the lens configuration of the embodiment willbe described with reference to the illustrative sectional view ofNumerical Data Example 1.

As shown in FIG. 1, the imaging lens of the embodiment includes a firstlens L1 having negative refractive power, a second lens L2 havingnegative refractive power, a third lens L3 having positive refractivepower, an aperture stop ST, a fourth lens L4 having positive refractivepower, and a fifth lens L5 having negative refractive power, arranged inthe order from an object side to an image plane side. A filter 10 may beprovided between the fifth lens L5 and an image plane IM. The filter 10may be optionally omitted.

According to the imaging lens of the embodiment, each of the first lensL1 to the fourth lens L4 are made of materials having Abbe's numbers ofbetween 45 and 75. On the other hand, the fifth lens L5 is made of amaterial having Abbe's number of between 20 and 40. More specifically,when the first lens L1 has Abbe's number νd1, the second lens L2 hasAbbe's number νd2, the third lens L3 has Abbe's number νd3, the fourthlens L4 has Abbe's number νd4, and the fifth lens L5 has Abbe's numberνd5, the imaging lens of the embodiment satisfies the followingconditional expressions:

45<νd1<7545<νd2<7545<νd3<7545<νd4<7520<νd5<40

The first lens L1 is formed in a shape, such that a curvature radius r1of an object-side surface thereof and a curvature radius r2 of an imageplane-side surface thereof are both positive, so as to a shape of ameniscus lens directing a convex surface thereof to the object side nearthe optical axis X. According to the embodiment, the first lens L1 isformed in a shape of a meniscus shape directing strongly concavedsurface to the image plane side.

The second lens L2 is formed in a shape, such that a curvature radius r3of an object-side surface thereof and a curvature radius r4 of an imageplane-side surface thereof are both positive, so as to have a shape of ameniscus lens directing a convex surface thereof to the object side nearthe optical axis X. Among them, the object-side surface of the secondlens L2 is formed as an aspheric shape, so as to direct a convex surfacethereof to the object side near the optical axis X and direct theconcave surface thereof to the object side at the periphery of the lens.In short, according to the embodiment, the second lens L2 is formed in ashape of a meniscus lens directing a convex surface thereof to theobject side near the optical axis X, and formed in a shape of abiconcave lens at the periphery of the lens, which is away from theoptical axis X.

The third lens L3 is formed in a shape, such that a curvature radius r5of an object-side surface thereof is positive and a curvature radius r6of an image plane-side surface thereof is negative, and formed in ashape of a biconvex lens near the optical axis X.

The fourth lens L4 is formed in a shape, such that a curvature radius r7of the object-side surface thereof is positive and a curvature radius r8of an image plane-side surface thereof is negative, and formed in ashape of a biconvex lens near the optical axis X. In addition, the fifthlens L5 is formed in a shape, such that a curvature radius r9 of anobject-side surface thereof and a curvature radius r10 of an imageplane-side surface thereof are both negative, and has a shape of ameniscus lens directing a concave surface thereof to the object sidenear the optical axis X.

Furthermore, the imaging lens of the embodiment satisfies the followingconditional expressions. Therefore, according to the imaging lens of theembodiment, it is possible to achieve both widening an angle of view ofthe imaging lens and satisfactory aberration correction.

−1.5<f5/f<−0.5  (1)

−3.5<f1/f<−1.5  (2)

1.0<f1/f2<1.5  (3)

0.5<f3/f<2.5  (4)

0.5<dA/f<1.0  (5)

In the above conditional expressions:

f: Focal length of the whole lens systemf1: Focal length of a first lens L1f2: Focal length of a second lens L2f3: Focal length of a third lens L3f5: Focal length of a fifth lens L5dA: Distance on an optical axis between the second lens L2 and the thirdlens L3

Furthermore, the imaging lens of the embodiment preferably satisfies thefollowing conditional expression (6):

1.5<f45/f<3.5  (6)

In the above expression,

f45: Composite focal length of the fourth lens L4 and the fifth lens L5

When the imaging lens satisfies the conditional expression (6), it ispossible to set refractive powers of the lenses disposed from theaperture stop ST to the image plane side. In the lens configuration ofthe imaging lens, the fourth lens L4 and the fifth lens L5 primarilycorrect chromatic aberrations. When the imaging lens satisfies theconditional expression (6), it is possible to more satisfactorilycorrect the chromatic aberrations. Here, it is not necessary to satisfyall of the conditional expressions, and it is achievable to obtain aneffect corresponding to the respective conditional expression when anysingle one of the conditional expressions is individually satisfied.

In the embodiment, all lens surfaces of each lens are formed as anaspheric surface. When the aspheric surfaces applied to the lenssurfaces have an axis Z in a direction of the optical axis, a height Hin a direction perpendicular to the optical axis, a conical coefficientk, and aspheric coefficients A₄ and A₆, a shape of the aspheric surfacesof the lens surfaces is expressed as follows:

$\begin{matrix}{Z = {\frac{\frac{H^{2}}{R}}{1 + \sqrt{1 - {\left( {k + 1} \right)\frac{H^{2}}{R^{2}}}}} + {A_{4}H^{4}} + {A_{6}H^{6}}}} & \left\lbrack {{Formula}\mspace{14mu} 1} \right\rbrack\end{matrix}$

Next, Numerical Data Examples of the imaging lens of the embodiment willbe described. In each Numerical Data Example, f represents a focallength of the whole lens system, Fno represents an F number, and ωrepresents a half angle of view, respectively. In addition, i representsa surface number counted from the object side, r represents a curvatureradius, d represents a distance between lens surfaces (surface spacing)on the optical axis, nd represents a refractive index for a d line, andνd represents Abbe's number for the d line, respectively.

Here, aspheric surfaces are indicated with surface numbers i affixedwith * (asterisk). In addition, a sum of surface spacing on the opticalaxis (length in air) from the object-side surface of the first lens L1to the image plane IM is indicated as La.

Numerical Data Example 1

Basic data are shown below.

f = 2.32 mm, Fno = 2.2, ω = 85.0° Unit: mm Surface Data Surface Number ir d nd νd (Object) ∞ ∞  1* 26.566 0.600 1.535 56.1 (=νd1)  2* 3.1091.272  3* 4.375 0.600 1.535 56.1 (=νd2)  4* 1.806 1.957 (=dA)  5* 3.3961.316 1.535 56.1 (=νd3)  6* (Stop) −4.285 0.877  7* 3.485 1.600 1.53556.1 (=νd4)  8* −1.888 0.100  9* −1.747 0.350 1.634 23.9 (=νd5) 10*−14.142 0.700 11 ∞ 0.700 1.517 64.1 12 ∞ 1.484 (Image ∞ plane) f1 =−6.64 mm f2 = −6.26 mm f3 = 3.77 mm f4 = 2.55 mm f5 = −3.18 mm La =11.32 mm Aspheric Surface Data First Surface k = 0.000, A₄ = −3.355E−04,A₆ = 1.813E−05 Second Surface k = 0.000, A₄ = 4.435E−03, A₆ = 1.144E−03Third Surface k = 0.000, A₄ = −4.839E−02, A₆ = 3.532E−03 Fourth Surfacek = 0.000, A₄ = −7.570E−02, A₆ = 5.541E−03 Fifth Surface k = 0.000, A₄ =−1.551E−02, A₆ = −2.427E−03 Sixth Surface k = 0.000, A₄ = −2.195E−02, A₆= 1.849E−03 Seventh Surface k = 0.000, A₄ = −2.487E−02, A₆ = −2.233E−03Eighth Surface k = 0.000, A₄ = 1.784E−02, A₆ = 2.153E−03 Ninth Surface k= 0.000, A₄ = 4.608E−02, A₆ = −3.862E−04 Tenth Surface k = 0.000, A₄ =2.056E−02, A₆ = −6.426E−03The values of the respective conditional expressions are as follows:f5/f=−1.37f1/f=−2.87f1/f2=1.06f3/f=1.63dA/f=0.85f45/f=3.18

Accordingly, the imaging lens of Numerical Data Example 1 satisfies theabove-described conditional expressions. Therefore, according to theimaging lens, it is possible to satisfactorily correct aberrations inspite of the wide angle thereof.

FIG. 2 shows a lateral aberration that corresponds to a half angle ofview co in the imaging lens of Numerical Data Example 1, which isdivided into a tangential direction and a sagittal direction (which isthe same in FIGS. 5, 8, 11, and 14). Furthermore, FIG. 3 shows aspherical aberration (mm), an astigmatism (mm), and a distortion (%),respectively. In the aberration diagrams, for the lateral aberrationdiagrams and spherical aberration diagrams, aberrations at eachwavelength, i.e. a g line (435.84 nm), an e line (546.07 nm), and a Cline (656.27 nm) are indicated. In the astigmatism diagram, anaberration on a sagittal image surface S and an aberration on atangential image surface T are respectively indicated (which are thesame in FIGS. 6, 9, 12, and 15). As shown in FIGS. 2 and 3, according tothe imaging lens of Numerical Data Example 1, the aberrations aresatisfactorily corrected.

Numerical Data Example 2

Basic data are shown below.

f = 3.02 mm, Fno = 3.1, ω = 85.0° Unit: mm Surface Data Surface Number ir d nd νd (Object) ∞ ∞  1* 84.529 0.450 1.535 56.1 (=νd1)  2* 2.7700.850  3* 6.436 0.615 1.535 56.1 (=νd2)  4* 1.854 1.669 (=dA)  5* 3.5321.327 1.535 56.1 (=νd3)  6* (Stop) −5.113 0.970  7* 3.758 1.242 1.53556.1 (=νd4)  8* −1.909 0.100  9* −1.767 0.337 1.634 23.9 (=νd5) 10*−11.803 0.700 11 ∞ 0.700 1.517 64.1 12 ∞ 3.567 (Image ∞ plane) f1 =−5.36 mm f2 = −5.11 mm f3 = 4.12 mm f4 = 2.56 mm f5 = −3.32 mm La =12.29 mm Aspheric Surface Data First Surface k = 0.000, A₄ = 4.189E−04,A₆ = 5.720E−05 Second Surface k = 0.000, A₄ = 5.528E−03, A₆ = 8.078E−04Third Surface k = 0.000, A₄ = −5.022E−02, A₆ = 4.100E−03 Fourth Surfacek = 0.000, A₄ = −7.165E−02, A₆ = 8.411E−03 Fifth Surface k = 0.000, A₄ =−1.130E−02, A₆ = −1.217E−03 Sixth Surface k = 0.000, A₄ = −2.008E−02, A₆= 1.895E−03 Seventh Surface k = 0.000, A₄ = −2.164E−02, A₆ = −1.941E−03Eighth Surface k = 0.000, A₄ = 2.324E−02, A₆ = 4.284E−04 Ninth Surface k= 0.000, A₄ = 5.041E−02, A₆ = −1.857E−03 Tenth Surface k = 0.000, A₄ =2.210E−02, A₆ = −5.974E−03The values of the respective conditional expressions are as follows:f5/f=−1.10f1/f=−1.78f1/f2=1.05f3/f=1.37dA/f=0.55f45/f=2.52

Accordingly, the imaging lens of Numerical Data Example 2 satisfies theabove-described conditional expressions. Therefore, according to theimaging lens, it is possible to satisfactorily correct aberrations inspite of the wide angle thereof.

FIG. 5 shows the lateral aberration that corresponds to a half angle ofview co in the imaging lens of Numerical Data Example 2. FIG. 6 shows aspherical aberration (mm), an astigmatism (mm), and a distortion (%),respectively. As shown in FIGS. 5 and 6, according to the imaging lensof Numerical Data Example 2, the aberrations are satisfactorilycorrected.

Numerical Data Example 3

Basic data are shown below.

f = 2.82 mm, Fno = 2.7, ω = 85.0° Unit: mm Surface Data Surface Number ir d nd νd (Object) ∞ ∞  1* 15.000 0.600 1.535 56.1 (=νd1)  2* 3.3430.638  3* 3.903 0.600 1.535 56.1 (=νd2)  4* 1.813 1.556 (=dA)  5* 4.3381.135 1.535 56.1 (=νd3)  6* (Stop) −5.834 0.853  7* 3.240 1.356 1.53556.1 (=νd4)  8* −1.877 0.085  9* −1.830 0.300 1.634 23.9 (=νd5) 10*−6.420 0.700 11 ∞ 0.700 1.517 64.1 12 ∞ 2.177 (Image ∞ plane) f1 = −8.19mm f2 = −7.03 mm f3 = 4.84 mm f4 = 2.45 mm f5 = −4.14 mm La = 10.46 mmAspheric Surface Data First Surface k = 0.000, A₄ = −2.242E−03, A₆ =1.294E−04 Second Surface k = 0.000, A₄ = 2.039E−03, A₆ = 5.002E−04 ThirdSurface k = 0.000, A₄ = −5.092E−02, A₆ = 3.136E−03 Fourth Surface k =0.000, A₄ = −7.343E−02, A₆ = 4.920E−03 Fifth Surface k = 0.000, A₄ =−1.474E−02, A₆ = 9.732E−04 Sixth Surface k = 0.000, A₄ = −2.884E−02, A₆= 4.104E−03 Seventh Surface k = 0.000, A₄ = −2.625E−02, A₆ = −2.489E−03Eighth Surface k = 0.000, A₄ = 2.021E−02, A₆ = 2.992E−03 Ninth Surface k= 0.000, A₄ = 4.532E−02, A₆ = −2.776E−05 Tenth Surface k = 0.000, A₄ =2.245E−02, A₆ = −6.487E−03

The values of the respective conditional expressions are as follows:

f5/f=−1.47f1/f=−2.90f1/f2=1.16f3/f=1.71dA/f=0.55f45/f=1.74

Accordingly, the imaging lens of Numerical Data Example 3 satisfies theabove-described conditional expressions. Therefore, according to theimaging lens, it is possible to satisfactorily correct aberrations inspite of the wide angle thereof.

FIG. 8 shows the lateral aberration that corresponds to a half angle ofview co in the imaging lens of Numerical Data Example 3. FIG. 9 shows aspherical aberration (mm), an astigmatism (mm), and a distortion (%),respectively. As shown in FIGS. 8 and 9, according to the imaging lensof Numerical Data Example 3, the aberrations are satisfactorilycorrected.

Numerical Data Example 4

Basic data are shown below.

f = 2.09 mm, Fno = 2.6, ω = 85.0° Unit: mm Surface Data Surface Number ir d nd νd (Object) ∞ ∞  1* 123.922 0.600 1.535 56.1 (=νd1)  2* 3.0061.456  3* 6.933 0.600 1.535 56.1 (=νd2)  4* 1.984 1.996 (=dA)  5* 4.4323.587 1.535 56.1 (=νd3)  6* (Stop) −4.718 0.461  7* 3.176 1.600 1.53556.1 (=νd4)  8* −1.909 0.100  9* −1.835 0.350 1.634 23.9 (=νd5) 10*−33.082 0.700 11 ∞ 0.700 1.517 64.1 12 ∞ 2.411 (Image ∞ plane) f1 =−5.77 mm f2 = −5.43 mm f3 = 4.95 mm f4 = 2.50 mm f5 = −3.08 mm La =14.32 mm Aspheric Surface Data First Surface k = 0.000, A₄ = 1.293E−03,A₆ = −3.312E−05 Second Surface k = 0.000, A₄ = 3.961E−03, A₆ = 2.003E−04Third Surface k = 0.000, A₄ = −4.747E−02, A₆ = 4.309E−03 Fourth Surfacek = 0.000, A₄ = −6.486E−02, A₆ = 5.650E−03 Fifth Surface k = 0.000, A₄ =−7.403E−03, A₆ = −2.905E−05 Sixth Surface k = 0.000, A₄ = −2.456E−02, A₆= 6.005E−03 Seventh Surface k = 0.000, A₄ = −3.361E−02, A₆ = 1.761E−03Eighth Surface k = 0.000, A₄ = 1.734E−02, A₆ = 3.224E−03 Ninth Surface k= 0.000, A₄ = 4.374E−02, A₆ = −2.928E−03 Tenth Surface k = 0.000, A₄ =1.183E−02, A₆ = −6.918E−03

The values of the respective conditional expressions are as follows:

f5/f=−1.47f1/f=−2.76f1/f2=1.06f3/f=2.37dA/f=0.95f45/f=3.34

Accordingly, the imaging lens of Numerical Data Example 4 satisfies theabove-described conditional expressions. Therefore, according to theimaging lens, it is possible to satisfactorily correct aberrations inspite of the wide angle thereof.

FIG. 11 shows the lateral aberration that corresponds to a half angle ofview co in the imaging lens of Numerical Data Example 4. FIG. 12 shows aspherical aberration (mm), an astigmatism (mm), and a distortion (%),respectively. As shown in FIGS. 11 and 12, according to the imaging lensof Numerical Data Example 4, the aberrations are satisfactorilycorrected.

Numerical Data Example 5

Basic data are shown below.

f = 2.70 mm, Fno = 2.4, ω = 85.0° Unit: mm Surface Data Surface Number ir d nd νd (Object) ∞ ∞  1* 17.169 0.600 1.535 56.1 (=νd1)  2* 3.7910.850  3* 4.328 0.600 1.535 56.1 (=νd2)  4* 1.815 2.284 (=dA)  5* 4.0781.336 1.535 56.1 (=νd3)  6* (Stop) −3.905 0.948  7* 3.397 1.198 1.53556.1 (=νd4)  8* −1.789 0.069  9* −1.687 0.349 1.634 23.9 (=νd5) 10*−66.371 0.700 11 ∞ 0.700 1.517 64.1 12 ∞ 1.932 (Image ∞ plane) f1 =−9.24 mm f2 = −6.37 mm f3 = 3.96 mm f4 = 2.38 mm f5 = −2.74 mm La =11.33 mm Aspheric Surface Data First Surface k = 0.000, A₄ = −7.831E−04,A₆ = 5.038E−05 Second Surface k = 0.000, A₄ = 1.056E−02, A₆ = 6.703E−04Third Surface k = 0.000, A₄ = −4.545E−02, A₆ = 3.313E−03 Fourth Surfacek = 0.000, A₄ = −7.999E−02, A₆ = 6.665E−03 Fifth Surface k = 0.000, A₄ =−1.669E−02, A₆ = −3.930E−03 Sixth Surface k = 0.000, A₄ = −2.475E−02, A₆= 1.566E−03 Seventh Surface k = 0.000, A₄ = −2.968E−02, A₆ = −4.230E−03Eighth Surface k = 0.000, A₄ = 1.775E−02, A₆ = 3.028E−03 Ninth Surface k= 0.000, A₄ = 5.003E−02, A₆ = −6.319E−05 Tenth Surface k = 0.000, A₄ =1.433E−02, A₆ = −7.012E−03

The values of the respective conditional expressions are as follows:

f5/f=−1.01f1/f=−3.43f1/f2=1.45f3/f=1.47dA/f=0.85f45/f=3.40

Accordingly, the imaging lens of Numerical Data Example 5 satisfies theabove-described conditional expressions. Therefore, according to theimaging lens, it is possible to satisfactorily correct aberrations inspite of the wide angle thereof.

FIG. 14 shows the lateral aberration that corresponds to a half angle ofview co in the imaging lens of Numerical Data Example 5. FIG. 15 shows aspherical aberration (mm), an astigmatism (mm), and a distortion (%),respectively. As shown in FIGS. 14 and 15, according to the imaging lensof Numerical Data Example 5, the aberrations are satisfactorilycorrected.

Here, in any of the above-described Numerical Data Examples, a surfaceof each lens is formed as an aspheric surface, but it is also possibleto form all or a part of the lens surfaces of the lenses that composethe imaging lens as spherical surfaces, as long as it is allowed in viewof the total length of the imaging lens and required opticalperformances.

Therefore, applying the imaging lens of the embodiment in an imagingoptical system such as cellular phones, digital still cameras, portableinformation terminals, monitoring cameras, onboard cameras, and networkcameras, it is possible to provide a small camera with satisfactorilycorrected aberrations in spite of a wide angle thereof.

The present invention may be applied in a device that requiressatisfactory aberration correcting ability as well as a wide imagingangle of view as an imaging lens, for example, in an imaging lens formounting in a device such as a cellular phone, a security camera, aonboard camera.

The disclosure of Japanese Patent Application No. 2012-237727, filed onOct. 29, 2012, is incorporated in the application by reference.

While the present invention has been explained with reference to thespecific embodiments of the present invention, the explanation isillustrative and the present invention is limited only by the appendedclaims.

What is claimed is:
 1. An imaging lens comprising: a first lens havingnegative refractive power; a second lens having negative refractivepower; a third lens having positive refractive power; a fourth lenshaving positive refractive power; and a fifth lens having negativerefractive power, arranged in this order from an object side to an imageplane side, wherein said first lens is formed in a shape so that asurface thereof on the object side and a surface thereof on the imageplane side have positive curvature radii, said second lens is formed ina shape so that a surface thereof on the object side and a surfacethereof on the image plane side have positive curvature radii, saidthird lens is formed in a shape so that a surface thereof on the objectside has a positive curvature radius and a surface thereof on the imageplane side has a negative curvature radius, said fourth lens is formedin a shape so that a surface thereof on the object side has a positivecurvature radius and a surface thereof on the image plane side has anegative curvature radius, said fifth lens is formed in a shape so thata surface thereof on the object side and a surface thereof on the imageplane side have negative curvature radii, said first lens, said secondlens, said third lens, and said fourth lens are formed of a materialhaving an Abbe's number between 45 and 75, said fifth lens are formed ofa material having an Abbe's number between 20 and 40, and said fifthlens has a focal length f5 so that the following conditional expressionis satisfied:−1.5<f5/f<−0.5 where f is a focal length of a whole lens system.
 2. Theimaging lens according to claim 1, wherein said first lens has a focallength f1 and said second lens has a focal length f2 so that thefollowing conditional expressions are satisfied:−3.5<f1/f<−1.51.0<f1/f2<1.5 where f is a focal length of a whole lens system.
 3. Theimaging lens according to claim 1, wherein said second lens has thesurface on the object side formed in an aspheric shape so that a convexsurface thereof faces the object side near an optical axis thereof and aconcave surface thereof faces the object side at a periphery thereof. 4.The imaging lens according to claim 1, wherein said third lens has afocal length f3 and said second lens is situated away from the thirdlens by a distance dA on an optical axis thereof so that the followingconditional expressions are satisfied:0.5<f3/f<2.50.5<dA/f<1.0.